The dexterity of the human hand enables it to execute complex and agile movements. Simulated movement of the human hand thus desirably achieves movement in directions having degrees of freedom similar to those in the human hand. Robotic simulation of movement in the human hand is practically limited by the size and weight of the components needed to simulate movement. The size of a robotic hand has conventionally suffered at the expense of obtaining the desired motion, and the desired dexterity of fingers and a thumb are achieved in a complex mechanism which still has limited capabilities. The action of these components does not closely approximate the desired movement of a human hand, and thus control of the robotic hand by a "smart glove" is less accurate.
Robotic devices simulating movement of the human hand frequently tend to sacrifice one or more desired simulated functions for other desired simulated functions. Many robotic hand devices focus on simulating the overall appearance and movement of the human hand while neglecting other equally important features such as the size, weight, mobility and control of the robotic device. Conventional robotic devices are therefore relatively complex, large, cumbersome and difficult to use. The complexity of conventional robotic devices also has resulted in robotic hands which are expensive to manufacture, and are also expensive to maintain.
U.S. Pat. No. 4,986,723 to Maeda and U.S. Pat. No. 5,447,403 to Engler, Jr. each describe a conventional robotic hand. Maeda describes a robot arm that comprises four flexible fingers and a thumb wherein each flexible finger and thumb includes three joints. Pulleys are provided on each joint so that each joint can be bent. The third joint has approximately one-half the bending motion of the second joint. The robot arm described by Maeda offers 18 degrees of freedom that resembles movement of a human arm. As a result, 18 actuators or motors are required to operate this cable wire and pulley system of Maeda. Similarly, Engler, Jr. describes a dexterous programmable robot and control system that includes a hand with four fingers and a thumb. Each finger and thumb have four degrees of freedom which are driven by a cable and pulley system not unlike Maeda. Both Maeda and Engler, Jr. rely upon a complex mechanical drive train to affect bending and rotational movement in the joints provided in the fingers and thumb. As a result, the robotic hands described by Maeda and Engler, Jr. are unreasonably large, heavy and cumbersome, making it difficult to grasp and control delicate or light objects with reasonable precision.
Other conventional robotic devices attempting to simulate movement of the human hand are described by U.S. Pat. No. 4,046,262 to Vykukal et al.; U.S. Pat. No. 4,350,381 to Hellmann; U.S. Pat. No. 4,921,293 to Ruoff et al.; U.S. Pat. No. 5,378,033 to Guo et al.; U.S. Pat. No. 5,347,490 to Mimura et al.; U.S. Pat. No. 5,476,357 to Arai; U.S. Pat. No. 5,570,920 to Crisman et al.; and U.S. Pat. No. 5,588,688 to Jacobson et al. These conventional devices are quite complex and thus expensive, and also are limited by many of the disadvantages described above.
Accordingly, there is a specific need for a dexterous robotic hand that closely resembles the anatomical movement of the human hand yet is lightweight, mobile and capable of grasping both heavy and light object s with precision.